High melting omega-amino carboxylic copolyamides



HIGH MELTING OMEGA-AMINO CARBOXYLIC COPOLYAMIDES John R. Caldwell andRussell Gilkey, Kingsport, Tenn, assignors to Eastman Kodak Company,Rochester, N.Y., a corportion of New Jersey N Drawing. Filed Jan. 24,1957, Ser. No. 635,958

13 Claims. (Cl. 260-78) This invention relates to improved linear highlypolymeric fiber-forming copolyamides formed by the condensation of from1 to 3 isomers of an aliphatic bifunctional omega-amino carboxyliccompound containing from 5 to 12 carbon atoms (e.g. 6-amino caproic acidor the corresponding lactam, namely, epsilon caprolactam) which isco-condensed with adipic acid and a bifunctional diamine selected fromthe group consisting of para-xylene-a,a'-diamine and 1,4-cyclohexanebis- (methylamine) which includes the cis or the trans isomers ormixtures thereof. The preferred copolyamides of this invention containfrom 50 to about 70 mole percent of the omega-amino carboxylic compound.

This invention provides an up-grading of the polyamides of the classformed from an omega-amino carboxylic compound. Of this class ofpolymers 6-nylon also called Perlon L is now commercially available; itsoftens at about 195200 C. and melts at about 205 to 215 C. As a resultof the up-grading of such a polyamide according to this invention, novelcopolyamides are formed which have melting points of from about 220 C.up to about 300 C. and can be formed into clear films and moldedobjects, can be extruded to form excellent fibers, and are generallyuseful for any of the purposes for which 6-nylon or nylon 66 is known tobe useful.

In contrast to 6-nylon or nylon 66, these novel copolyamides haveimproved dyeability, broader softening temperature range, higher tensilemodulus, and other improved physical and chemical characteristics.

In this specification omega-aminocarboxylic acids an correspondinglactams are generically referred to as omega-aminocarboxylic compounds.The employment of a 6-aminocaproic compound in the formation ofpolyamides such as Perlon L or 6-nylon on a commercial scale has beenonly partially successful since there are many instances where a highermelting point is desirable. For general textile use, it is important tohave a melting point that is about 240 C. or higher and a softeningtemperature of at least about 220 C. Nylon 66 has asoftening-temperature around 220 C. and a melting point of about 265 C.

The prior art discloses various copolyamides formed from variouscomponents including 6-aminocaproic acid or its lactam which have beencharacterized by even lower melting points and softening temperatures,hence they are obviously not of commercial promise for general textileuse. For example, a copolyamide from 6-aminocaproic acid, adipic acid,and hexamethylenediamine has been prepared and found to have meltingpoints well below those of 6-nylon. Thus, the presence of 30-40% ofadipic acid and hexamethylenediamine in this copolyamide depressed themelting point to about 170 C. A similar result was obtained with acopolymer of 6-aminocaproic acid plus hexamethylenediamine andterephthalic acid. For example, the presence of 20-30% of theterephthalic acid-hexamethylenediamine component also depressed themelting point to about 170 C. These retates Patent C 0 2,985,627Patented May 23, 1961 ICC sults are in accordance with the widelyaccepted rule developed by Flory which states that interpolymers meltlower than the pure homopolymer, that is, if component A was addedduring the formation of polymer B, the melting point of polymer B wouldbe depressed according to the molecular proportion of A. This rule isdiscussed at considerable length by Flory in J. .Am. Chem. Soc. 72 2024(1950). See also J. Chem. Phys. 17 223 (1949). The theoreticalderivation is given for this rule along with considerable experimentalverification. This melting point rule has been widely accepted in thefield of polymer science and it is often called Florys Melting PointLaw. The general validity of this rule has been established forpolyesters, polyamides and vinyl polymers. The polyamides of thisinvention represent an unexpected exception to Florys rule and therebyadd an important contribution to the art which also has considerableeconomic value because the polyamides of G-aminocaproic compounds andrelated compounds can be up-graded and their utility thereby greatlyincreased.

Various modifiers of polycaproamide polymers, along with the meltingpoint of the resulting copolyamide (the homopolyamide melts at about 210C.), are given below in order to illustrate a few examples of thisinvention in tabular form:

Melting Point of Copolyamides, C.

Mole percent B-aminohexanolc acid Modified with Modified withadip1e+1,4- adipic+peyclohexanexylene-a tbis (methyldiamlne amine)Calculations based on data in Faserforschung and Textiltechnik, 6, 2 77(1955), indicate that corresponding copolyamides modified with adipicacid+hexamethylenediamine would melt at temperatures well below 200 C.;'thus, the copolyamides of this invention melt at temperatures which arefrom about 50-90 higher. This is most unexpected for the reasonsdiscussed hereinabove.

it is an object of this invention to provide a linear, highly polymericfiber-forming copolyamide derived for the most part from thecondensation of an omega-aminocarboxylic compound with an up-gradingcomponent whereby the copolyamides have higher melting points than thehomopolyamides derived from the omega-'aminocarprocess for preparingcopolyamides of an omega-aminocarboxylic compound wherein the processfor preparing a ho'mopolyamide is modified by incorporatinga'substantial proportion of an tip-grading dicarboxy compound and anup-grading diamine.

A particularly valuable object of this invention pertains to theupgrading of these polyamides derived from branched chainomega-aminocarboxylic compounds.

A further object of this invention is to provide fibers, films, moldedobjects, compositions, and other materials of improved utility.

Additional objects will become apparent hereinafter.

According to a principal embodiment of this invention we have found thatthe class of linear highly polymeric fiber-forming polymers formed bythe condensation of an aliphatic bifunctional omega-aminocarboxyliccom-- pound containing from 5 to 12 carbon atoms, can be greatlyimproved by having incorporated into this class of polymers from about20 to 25 up to about 45 to 50 mole percent of polyamide componentsderived from adipic acid and a bifunctional diamine selected from thegroup consisting of p-xylene-a,o;'-diamine, trans-1,4-cyolohexanebis(.methylamine) and cis l,4'cyclohexane bis- (methylamine).

- These up-graded polyamides can be advantageously produced by a processwhich comprises condensing 6- aminocaproic acid or the lactam thereof orthe indicated homologs thereof containing from to 12 carbon atoms, withadipic acid and an equimolecular proportion of a bifunctional diamineselected from the group just described. Alternatively, a salt canbeformed from the adipic acid and one of the bifunc-tional diamines justdescribed and this salt heated with G-aminocaproic acid or itslactam orhomolog thereof so as=to form the copolyamide in accordance with thisinvention. Other processes can also be employed.

The techniques which can be employed for the preparation'of suchcopolyamides are known in the art andneed no detailed elaboration inthis specification. Some of the techniques which can be employedare-illustrated'in the various examples which are set forth hereinbelow.

Valuable copolyamides can be producedin accordance with this inventionwhich give clear films and molded objects, have melting points of 200 C.or higher, have excellent=dyeability, soften over a broad range oftemperatures aswide as from to 20, and possess essentially all of thevaluable characteristics otherwise possessed by homopolyamide formedfrom 6-aminocaproic acid, its lactam or homologs thereof; thus, fibersmade from the upgraded polymers of this invention have excellentphysical properties such as tensile strength, elongation, elasticity,etc.

One of the most noticeable improvements which the 6- aminocaproiccopolyamides of this invention have in contrast to the homopo-lyamidesof 6-aminocaproic acid or its lactam is based upon the fact that thehomopolyamide has a strong tendency to crystallize and become opaquewhen molded orpressed into sheets, whereas the upgraded copolyamidespossess the opposite tendency toward giving clear. films and moldedobjects.

It is most obvious that the products of this invention have suchexcellent physical and chemical characteristics in contrast to those ofthe homopolyamide. The copolyamides wherein the bifunctional amine istrans-1,4-cyclohexanebis(methylamine) are polymers of exceptional valueand can be considered in a class by themselves having melting points inthe range of about 245 C. or higher. As. a practical matter, it isgenerally advantageous to employ mixtures of the trans and cis isomers.Hence, the examples given throughout this specification are based uponthe employment of such mixtures rather than only one of the isomers ofl,4-cyclohexanebis(methylamine). The namel,4-cyclohexanebis(methylamine) is the name preferred by ChemicalAbstracts Nomenclature. This compound can also be called1,4-di-(aminomethyl)cyclohexane.

An' advantageous method for preparing the copolyamides of this inventionincludes heating the reactants at a temperature of from about 200 toabout 300 C. for several hours. Advantageously, the first stage of theheating cycle can be carried out under pressure in order to avoid theescape of volatile reactants. Thus, the first stage is preferablycarried out in a closed vessel such as an autoclave. The final stage ofthe polymerization can be advantageously performed at atmosphericpressure in an inert atmosphere or under a vacuum. Although theprocesses for preparing the copolyamides of this invention can beconducted employing the free acid, it is frequently advantageous toemploy the lactam. In accordance With a preferred embodiment of thisinvention, a salt is first prepared from equimolecular quantities of oneof the designated bifunctional diamines and adipic acid, This salt isthen advantageously heated with the acid or lactam in the desired ratio.

' textile fibers.

In the preparation of polyamides that melt higher than about 270 C., itis usuallypreferable to use the solid phase process. That is, aprepolymer'having an inherent viscosity of 0.20.4 is first made byheating the reactants at 2l0260 C. in a closed vessel in the presence ofwater. The prepolymer is then granulated or pulverized and heated in avacuum or inert atmosphere at a temperature somewhat below the meltingpoint until the desired viscosity is obtained. The preferredcompositions contain about 50-70 mole percent amino acid.

In general, any omega-amino acid that contains from 5 to 10 carbon atomsbetween the carboxyl group and amino group can be used. The carbon chaincan be straight or branched. Examples of straight chain amino acids aregiven by the general structure H N CH CO OH where n=510. The branchedchain acids can contain methyl or ethyl groups as substituents on themain carbon chain. The methyland ethyl-substituted 6-aminocaproic acidsare of particular importance because they are derived from low-costcresols, xylenols, and ethylphenol fractions that are obtained in coaltar and coal hydrogenation products. Heretofore, the amino acids madefrom the alkylated phenols were of no value because the sidechainslowered the melting point of the polyamides excessively.

An important object of this invention is to provide a method for.up-grading the .polyamides made from branched chain amino acids to givevaluable products that melt in the range advantageous for highly usefulplastics and in many cases in the range required for Although aminoacids containing methyl or ethylgroups are of value in the process ofthe invention, higher alkyl groups such aspropyl, isobutyl, and butylcan' be present. Suitablev examples of branched chain amino acidsinclude: 6-aminocaproic acid having a methyl or ethyl group in the2,3,4, or 5 position; 7- aminoheptanoic acid having a methyl. or ethylgroup on any carbon except the seventh; higher amino acids arerepresented by 4-ethyl-IO-aminodecanoic. acid,6-methylll-arninoundecanoic acid, etc; if two substituents are present,it is preferred but notessential that they be located on the same carbonatom in order to give a symmetrical structure as represented by3,3-dimethyl-6- aminocaproic acid and 4,4-dirnethyl-7-aminoheptanoicacid. The omega carbon atom preferably contains no additional alkylsubstituent. When it is desired to upgrade polyamides from branchedchain amino acids, melting points over 200 C. can generally be achievedby using 40-50 mole percent of the upgrading components of thisinvention; in any event, the up-grading effect is quite pronounced and avastly improved product is produced by following this invention.

Although it is preferred to use only one amino acid in the copolyamidesof the present invention, in some cases a mixture of two or three aminoacids can be employed. For example, satisfactory results can be obtainedby using the mixture of methyl-substituted 6-arninocaproic acids madefromv commercial cresylic acid which is'a mixture of 0-, m-, andp-cresol. The principal components are 3- and 4-methyl-6-aminocaproicacids.

This invention can be further illustrated by the following examples ofpreferred embodiments although it will be understoodthat these examplesare included merely for purposes of illustration and are not intended tolimit the scope of the invention unless otherwise specificallyindicated.

Example 1 The salt of adipic acid and 1,4-cyclohexanebis(methylamine) isespecially valuable for modifying 6-aminohexanoic acid polyamides. From33 to 50 mole percent of this component gives copolyamides that melt inthe range of 230-280 C. This high melting point is particularlysurprising since it is shown in the prior art that 40 mole percent ofadipic acid-hexamethylenediamine salt actually lowers the melting point.i I

A mixture of 0.60 molecular proportion of 6-aminohexanoic acid lactam(caprolactam) and 0.40 molecular proportion of the salt of adipic acidand 1,4-cyclohexanebis(methylamine) was placed in a stainless steelautoclave. The salt was added as 40% solution in water. The autoclavewas purged with nitrogen and further purged of air by heating to 120 C.and releasing a small amount of water vapor. The release valve was thenclosed and the autoclave was heated to 250 C. while maintaining apressure of 220+250 p.s.i. by releasing steam. The pressure was thenslowly bled to atmospheric and heating at 260' C. was continued for twohours. The resulting colorless polyamide was extruded from the autoclaveby nitrogen pressure. The inherent viscosity of the polymer as measuredin 60 phenol-40 tetrachlorethane was 0.78. The melting point as measuredunder crossed nicols on the hot stage of a microscope was 245-255 C.

Using the general method described above, other ratios of the adipicacid salt of 1,4-eyclhexanebis(methylamine) were used. The meltingpoints of the polymers are summarized below:

Melting Point Mole Percent fi-Aminohexanoic Acid of Copolyamide, C

It is seen that the presence of the adipic acid salt raises the meltingpoint substantially.

These copolyamides are moderately crystalline and can be spun intofibers which can be cold drawn and heat set under appropriateconditions. The fibers are readily dyeable with disperse dyes. Thecopolyamides are also valuable as molding materials. The relatively widemelting point range increases the ease of processing in extrusion.Clear, transparent molded articles are obtained due to the slower rateof crystallization of the copolyamide.

Example 2 The p-xylene-a,a'-diamine salt of adipic acid was used tomodify poly-6-aminohexanoic acid and thus produce a series of highmelting copolyamides. Polymers containing 33 and 45 mole percent of theadipic acid salt melted at 235-245 and 270-283 C., respectively.

Example 3 Example 4 The polyamide made from4,4-dimethyl-7-aminoheptanoic acid is difficult to crystallize and meltsin the range of 135-155 C. A copolyamide made from 0.55 mole4,4-dirnethyl-7-aminoheptanoic acid, 0.45 mole adipic acid, and 0.45mole 1,4-cyclohexanebis(methylarnine) melted at 185-200 C.

Example The polyamide from 4-methyl-6-aminohexanoic acid melts in therange of 170185 C. A copolyamide made from 0.55 mole4-methyl--aminohexanoic acid, 0.45 mole adipic acid, and 0.45 molep-xylene-ot,a'-diamine melted at 212223 C. Similar results can beobtained employing a mixture of isomers of methyl-6-aminohexanoic acidusing either p-xylene-a,a'-diamine or 1,4- cyclohexanebis(methylamine).The principal isomers employed are those where the methyl radical is inthe 3-position and 4-position.

All of the copolyamides described above can be made into fibers andfilms which can be oriented and heat set to form valuable materials forgeneral textile use and many other purposes such as wrapping materials,electrical insulation, etc. Moreover, useful molding and extrusionplastics are also provided by this invention and are superior to thoseobtained from 6-nylon and nylon 66 in several important respectsespecially at elevated temperatures and during processing operationswhere a broad softening range is desirable. The production of crystalclear products of advantageously high melting points is especiallynoteworthy. Transparent films can be produced which can be readily dyed.

Reference is made to the copending application filed by Bell et al.October 24, 1956, Serial No. 617,931, and additional applications filedconcurrently herewith by Caldwell et al. Serial Nos. 635,957 and 635,959which describe related improved polyamides.

Although the invention has been described in considerable detail withreference to certain embodiments thereof, it will be understood thatvariations and modifications can be effected without departing from thespirit and scope of the invention as described hereinabove and asdefined in the appended claims.

We claim:

1. A linear highly polymmeric copolyamide having a melting point of fromabout 200 to 300 C. of from to 50 mole proportions of an aliphaticbifunctional omega-aminocarboxylic acid containing from 5 to 12 carbonatoms, from 20 to 50 mole proportions of adipic acid and a correspondingnumber of mole proportions substantially equal to the mole proportionsof adipic acid of a bifunctional diamine selected from the groupconsisting of trans-1,4-cyciohexanebis(methylarnine) and cis-1,4-cyclohexanebis(methylamine) 2. A copolyamide as defined by claim 1of from 80 to 50 mole proportions of 6-aminocarproic acid, from 20 to 50mole proportions of adipic acid and an equiniolecular proportion oftrans 1,4-cyclohexanebis(methylamine).

3. A copolyamide as defined by claim 1 of from 80 to 50 mole proportionsof 6-aminocaproic acid, from 20 to 50 mole proportions of adipic acidand an equimolecular proportion of a mixture of trans and cisl,4-cyclonex anebis (methylamine) 4. A copolyamide as defined by claim 1of from 60 to 50 mole proportions of 7 aminoheptanoic acid, from 40 to50 mole proportions of adipic acid and an equimolecular proportion of1,4-cyclohexanebis(methylamine).

5. A copolyamide as defined by claim 3 of about 2 mole proportions ofo-aminohexanoic acid, 1 mole proportion of adipic acid and 1 moleproportion of mixed cis and trans isomers of1,4-cyclohexanebis(methylamine), characterized by melting at about231'-240 C.

6. A copolyamide as defined by claim 3 of about 0.55 mole proportion of6-aminohexauoic acid, 0.45 mole pro-' portion of adipic acid and 0.45mole proportion of mixed cis and trans isomers of 1,4-cyclohexanebis(methylamine) characterized by melting at about 260- 7. A process forpreparing a linear highly polymeric: copolyamide comprising heating fromabout 20 to about.

50 mole proportions of adipic acid, from about 80 to 50 atrans-1,4-cyclohexanebis(methylamine) and cis-1,4-cycl0- 2,241,321Schlack May .6, 1941 hexanebis(methylamine) whereby there is formed a2,252,555 Carothers Aug. 12, :1941 copolyamide melting at aboveabout-200-C. 2,625,536 Kirby Jan; 13, 1953 8. A film of a copolyamide asdefined in claim -1.

9. -A fiber of a copolyamide-as defined in claim 1. FOREIGN PATENTS 10.A film of a copolyamide as defined in claim 3. 87 3,983 France Apr. 13',1942 11. Afiber of a copolyarnide as defined in claim 3. 1,112,203France Nov; 9, 1955 12. A film of a copolyamide as defined in claim 4. V13. A fiber of a copolyamide as defined in claim 4; OTHER REFERENCES 10Hill et al.: J. Polymer Science, vol. 3 (1948), pp. References Cited inthe file of this patent 609, 2

UNITED STATES PATENTS 1 .et al.. J. Polymer Science, vol. 8 (1953), pp.2,130,523 Carothers Sept. 30', 1938" Evans et al.: J. American ChemicalSociety, vol. 72

2,130,948 Carothers Sept. 30, 1938' 15 (1950), pp. 2018-2028.

1. A LINEAR HIGH POLYMMERIC COPOLYAMIDE HAVING A MELTING POINT OF FROMABOUT 200* TO 300*C. OF FROM 80 TO 50 MOLE PROPORTIONS OF AN ALIPHATICBIFUNCTIONAL OMEGA-AMINOCARBOXYLIC ACID CONTAINING FROM 5 TO 12 CARBONATOMS, FROM 20 TO 50 MOLE PROPORTIONS OF ADIPIC ACID AND A CORRESPONDINGNUMBER OF MOLE PROPORTIONS SUBSTANTIALLY EQUAL TO THE MOLE PROPORTIONSOF ADIPIC ACID OF A BIFUNCTIONAL DIAMINE SELECTED FROM THE GROUPCONSISTING OF TRANS-1,4-CYCLOHEXANEBIS(METHYLAMINE) ANDCIS1,4-CYCLOHEXANEBIS(METHYLAMINE)